I've digitized hundreds of old family photos from 35mm slides from the 1960s and 1970s. There is in general a very vivid oversaturated look to all the colours, not just the sky. Primary colours likes reds, yellows, greens, blues, etc. just pop out. Which is actually great for photos of your childhood holidays, etc. No-one wants dull grey photos of that kind of thing. I suspect that the film makers did that deliberately, kind of like how old Technicolor movies have a very vivid saturation to the colours.

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I've noticed that the cheaper the camera nowadays, the brighter the colors. The more expensive digital SLRs now produce much flatter, but more accurate colors, but small pocket cameras often have a "vivid" setting more as a default. It simply makes your vacation photos look better.

I have it on "good authority" that the sky is blue NOT because of of our memories or because of Manganese di-Bromo di-Fluoro-Benzidine (salts).

It is blue from OZONE.

Ozone is a blue colored form of oxygen (it is what makes the sky blue), and unlike regular oxygen, it is composed of three oxygen atoms instead of two. It is the addition of the third oxygen atom that makes ozone “supercharged” oxygen, and gives it all of its remarkable medical properties. -

Long-term exposure to ozone has been shown to increase risk of death from respiratory illness. A study of 450,000 people living in United States cities showed a significant correlation between ozone levels and respiratory illness over the 18-year follow-up period. The study revealed that people living in cities with high ozone levels such as Houston or Los Angeles had an over 30% increased risk of dying from lung disease.

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Are these the "remarkable medical properties" to which the good Dr refers?

Are these the "remarkable medical properties" to which the good Dr refers?

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NOPE. It is only harmful if breathed. If taken in water or by injection it is about 30 different kinds of good for you. Fancy (and not cheap) clinics take a pint of your blood, add ozone while you watch then transfuse it back. It is tangentially related to the hydrogen hyperoxide cure. I'll do a thread on it when I get more time, or you're welcome to if you like.

It's not clear if you were joking, but the sky is not blue due to ozone, it's blue due to Rayleigh scattering from the nitrogen and oxygen. Nothing to do with ozone.

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Yeah, that occurred to me too.....since Rover pics from Mars (a planet with a VERY thin atmosphere in comparison to Earth's) show a blue sky as well. And, AFAIK Mars does not have an ozone layer similar to Earth's.

I will say, though, that Human visual perception is key, in this discussion. (And possible flawed memory). But, would certainly be interesting (to say the least) to be able to view the Martian sky with the unaided, naked eye. Ah well.....one can dream....

I said I had it on "good authority" in quotes, and then mentioned it is widely promoted for health benefits as well. I thought the varied fonts and colours would help too....and you thought I was serious? maybe we need a joke icon.

I said I had it on "good authority" in quotes, and then mentioned it is widely promoted for health benefits as well. I thought the varied fonts and colours would help too....and you thought I was serious? maybe we need a joke icon.

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LOL! (That, at least...though dated, is obvious). Much relief was had by all...........

I said I had it on "good authority" in quotes, and then mentioned it is widely promoted for health benefits as well. I thought the varied fonts and colours would help too....and you thought I was serious? maybe we need a joke icon.

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I said it was not clear if you were joking, i.e. not clear to everyone who might read this. We don't want to promote misconceptions by repeating them ironically.

The sky may not be less blue today than it used to be when the sky is clear, but we have clear blue skies less often because of the increase in cirrus coverage over North America and Europe. And invisible cirrus haze (which has become more common) does make the sky less blue. In that sense, I believe there is truth to the statement.

The sky may not be less blue today than it used to be when the sky is clear, but we have clear blue skies less often because of the increase in cirrus coverage over North America and Europe. And invisible cirrus haze (which has become more common) does make the sky less blue. In that sense, I believe there is truth to the statement.

You know that there are a lot of papers about cirrus trends in recent years. See e.g. Minnis P: "Contrails, cirrus trends, and climate" from 2004, followed up by a truckload of papers on the same topic.
In the 2004 paper, Minnis calculated the frequency of clear skies, and found that in the USA it decreases by 1.3% per decade. But that's the absolute change, not the relative change. Given that clear-sky coverage is about 40%, the relative decrease is about 3.2% per decade. That means that in the last 50 years, clear skies may have decreased by about 15% over the US. This is mostly caused by the increase in cirrus which is mostly due to contrails.

Found this circa 1940s (Believed to be of the 1944 Eruption of Mount Augustine, slide film used not specified) slide on the Alaska Volano observatory website, I'll admit I've no idea if they've digitally tweaked the image, but it also looked to my eyes as if it had been take more recently.

The paper implicates contrails in the decrease of clear days in areas of heavy air traffic:

The long-term trends give evidence of natural climate changes, whereas the localized shifts to more cloudiness in the central area since 1960 suggest anomalous changes related to jet-induced cirrus.

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Of course, industrial pollution, smog, etc. also contributed to the increase in cloudiness/haziness, and probably a less blue sky, or a decrease in the number of clear days when the sky is as blue as it used to be.

Global brightening in the last 20 years may have reversed this globally, but probably not everywhere locally.

I found this set on Flickr with a lot of photos from London Heathrow airport in the 1980s. I was looking to see if there were any good contrail shots. There aren't, but it's noticeable just how white/grey the sky is in a lot of the pictures even on "sunny" days. Certainly not the blue skies of nostalgia!

I found this set on Flickr with a lot of photos from London Heathrow airport in the 1980s. I was looking to see if there were any good contrail shots. There aren't, but it's noticeable just how white/grey the sky is in a lot of the pictures even on "sunny" days. Certainly not the blue skies of nostalgia!

I would just like to throw it out there, that I was fortunate to know a man that knew some men that maintained the flight simlators at Heathrow. I was informed for the cost of a bottle of whisky on any weekend, I could play the slot machines for an afternoon. Turned out our slot machine was the Trident 3.

Aside from the fact my sister crashed (tipped the wings on landing thinking it could be steered by the steering wheel as it went off course on the tarmac) and I ploughed through the runway barrier and halted on the perimeter road because I didn't know where the brakes were - we had a great time! I can boast, after the learning experience I successfully landed at Kai Tak first attempt, though the engineer glanced at the graph and uttered "...bit of a fighter approach but you got it down"

I wouldn't know. To me it is just another trijet, similar to one that I flew by regularly at the time.
This picture was taken in 1980, the year of Moscow Olympics. As one can see, the sky over my old country was bluer too

Just want to add: When the human eye grows older, it often looses some of it's capabilities. This can be associated with particular forms of illness, but even without major illness there is a degradation happening.
This is not limited to the tissue of eye itself, but can also be a form of age dependent neuro-degeneration.

this 18th century instrument designed to measure the blueness of the sky called a Cyanometer. The simple device was invented in 1789 by Swiss physicist Horace-Bénédict de Saussure and German naturalist Alexander von Humboldt who used the circular array of 53 shaded sections in experiments above the skies over Geneva, Chamonix and Mont Blanc. The Cyanometer helped lead to a successful conclusion that the blueness of the sky is a measure of transparency caused by the amount of water vapor in the atmosphere. You can learn more at the Royal Society of Chemistry.

Its not that the sky is a different color blue, its that there aren't any blue sky days anymore. Just a dull thin layer of contrails spreading in the form of grid pattern days. Right Mick?

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Just today we had a clear sky, with just a few clouds off to the south and east. Particularly noteworthy was the fact that what persistent contrails there were occurred only in very close proximity to the existing clouds, where the high RH would naturally be. Each appeared to end fairly abruptly at a consistent distance from the cloud proper, too.

Its not that the sky is a different color blue, its that there aren't any blue sky days anymore. Just a dull thin layer of contrails spreading in the form of grid pattern days. Right Mick?

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There are still plenty of blue sky days. When the air is dry, you won't see persistent contrails and the sky will be just as blue as in the past.

What may well be true is that days where conditions are suitable for cirrus formation will be somewhat cloudier nowadays than they would have been in the days before widespread air travel, especially in areas (like where I live) that see lots of overflights.

When the sky is clear, though, it's probably a lot clearer than it was 100 years ago, especially in cities, thanks to the reduction in smoke pollution from sources on the ground.

I have tried to illustrate the change in the sky's color according to Chuck Long's research. His research shows that the red-to-blue ratio, red measured at 870 nm and blue at either 415 or 500 nm, has increased by ~10% in 16 years. Unfortunately, 870 nm is infrared, which cannot be represented as an RGB color. So for simplicity, I just assumed that the R/B ratio in the sky color just increased by 10%. Also, his research shows a 4.5 W/m2 increase per decade in diffuse radiation, so in 16 years that is about 7 W/m2. Since the total radiation is about 1 kW/m2, this means a 0.7% increase. So I assumed that R+G+B would increase by 0.7%. This gave the following comparison:

Left half of the image is "sky blue", corresponding to RGB components (135,206,250). Right half is (145,206,244). This corresponds to a 10% increase in the red/blue ratio and a 0.7% increase in overall brightness.

Would you notice the difference? And if it occurred slowly over 16 years?

I have tried to illustrate the change in the sky's color according to Chuck Long's research. His research shows that the red-to-blue ratio, red measured at 870 nm and blue at either 415 or 500 nm, has increased by ~10% in 16 years. Unfortunately, 870 nm is infrared, which cannot be represented as an RGB color. So for simplicity, I just assumed that the R/B ratio in the sky color just increased by 10%. Also, his research shows a 4.5 W/m2 increase per decade in diffuse radiation, so in 16 years that is about 7 W/m2. Since the total radiation is about 1 kW/m2, this means a 0.7% increase. So I assumed that R+G+B would increase by 0.7%. This gave the following comparison:

Left half of the image is "sky blue", corresponding to RGB components (135,206,250). Right half is (145,206,244). This corresponds to a 10% increase in the red/blue ratio and a 0.7% increase in overall brightness.

Would you notice the difference? And if it occurred slowly over 16 years?

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Was Charles Long talking all days in general, or only days when contrails are forming,is there a day to day hold over of the ice crystals? Shouldn't the ice crystals fully sublimate on the days of low humidity at flight level?

Was Charles Long talking all days in general, or only days when contrails are forming,is there a day to day hold over of the ice crystals? Shouldn't the ice crystals fully sublimate on the days of low humidity at flight level?

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It's a yearly average over days classified as clear-sky conditions (no visible contrails). There can be a sub-visible cirrus haze that is still classified as clear sky.

It's a yearly average over days classified as clear-sky conditions (no visible contrails). There can be a sub-visible cirrus haze that is still classified as clear sky.

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thanks, that would still be days that are borderline or approaching conditions for contrail formation, wouldn't it? If it's too dry up there we are not going to see the cirrus haze, it really means we are seeing more days with haze, is that correct?

There is a thing called the Angstrom exponent https://en.wikipedia.org/wiki/Angstrom_exponent which gives a measure of aerosol size. This relates to attenuation of the sun (AOT) as a function of wavelength. Scattering is sort of the opposite, but since nothing (up there) is smaller is smaller than a molecule, any aerosol, or sub-visual cirrus, is going to make the sky whiter/less blue than the case with pure Rayleigh scattering.